Fault code SPN 3515 FMI 10 indicates a problem with the DEF quality sensor in vehicles equipped with a Cummins engine, such as Volvo trucks. This sensor measures both the temperature and quality of the DEF fluid.
In our workshop, we’ve encountered Fault Code SPN 3515 quite frequently, especially on European makes like Volvo and Mercedes-Benz trucks. Just last week, a 2019 Volvo VNL came in with the check engine light on, and sure enough, our diagnostic scan revealed SPN 3515 FMI 10. We traced the issue to a faulty DEF quality sensor, which was giving inaccurate readings and causing the DEF dosing to be off. Replacing the sensor solved the problem. We’ve also seen this code pop up on some Kenworth and Peterbilt trucks with Cummins engines, but it seems to be more prevalent on the European brands. Whenever this code appears, we know to focus our attention on the DEF system, particularly the quality sensor, wiring, and fluid condition.
Urgency and Driving Considerations
If you encounter this fault code, do not continue driving the vehicle. Driving with a faulty DEF quality sensor can lead to:
- Inaccurate DEF quality readings
- Improper DEF dosing
- Potential damage to the SCR system
It’s best to have the vehicle towed to a dealer or qualified repair shop to diagnose and fix the issue.
Code Specifics
SPN 3515 is a generic J1939 code that applies to various makes and models with Cummins engines, including:
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- Volvo trucks
- Kenworth trucks
- Peterbilt trucks
- Case IH agricultural equipment
The FMI (Failure Mode Indicator) provides more detail about the specific fault:
- FMI 10 = Abnormal rate of change
- Other potential FMIs: 3 (voltage high), 4 (voltage low), 2 (intermittent signal), etc.
Parts Involved
The key component is the combination DEF quality sensor, which typically integrates:
- DEF quality sensor
- DEF temperature sensor
- DEF level sensor
This sensor is located in the DEF tank and connects to the vehicle’s engine control module (ECM) via wiring.
Common Causes
Potential causes of an SPN 3515 FMI 10 fault include:
- Faulty DEF quality sensor
- Wiring issue between sensor and ECM
- Contaminated or degraded DEF fluid
- Extreme temperatures affecting sensor readings
- Rodent damage to wiring or sensor
Diagnosis Steps
To properly diagnose the root cause:
- Retrieve fault codes using a scan tool and record all codes present.
- Visually inspect the DEF quality sensor, wiring, and connectors for obvious damage.
- Test the sensor’s resistance and compare to specifications (typically 300-600 kΩ at room temp).
- If sensor tests OK, check DEF fluid with a refractometer to verify 32.5% urea concentration.
- If fluid tests OK, perform a wiggle test on wiring and connectors to check for intermittent faults.
Repair Solutions
Repairs will depend on the diagnosed root cause:
- Faulty sensor – replace the combination DEF quality sensor assembly
- Wiring issue – repair damaged wires or connectors
- Contaminated DEF – drain tank, flush system, and refill with new DEF fluid
- Rodent damage – repair chewed wires, install rodent deterrent tape
Prevention
To help prevent SPN 3515 faults:
- Only use API-certified DEF fluid from reputable suppliers
- Avoid storing DEF for longer than 12 months
- Keep the DEF tank and surrounding area clean
- Regularly inspect wiring and connectors
- Address any rodent issues promptly
Associated Costs
Repair costs will vary but may include:
- Diagnostic fee: $100-200 USD / €85-170 EUR
- Combination DEF sensor: $500-800 USD / €425-680 EUR
- DEF fluid: $3-6 USD per gallon / €2-5 EUR per 3.8 L
- Wiring repairs: $100-300 USD / €85-255 EUR
Related Faults
Other fault codes potentially related to SPN 3515 include:
- SPN 1761 – DEF tank temperature sensor
- SPN 3031 – DEF tank level sensor
- SPN 3226 – DEF pump
- SPN 4094 – Reductant system performance
Frequently Asked Questions about Fault Code SPN 3364
What is Fault Code SPN 3515?
Fault Code SPN 3515 indicates a problem with the Diesel Exhaust Fluid (DEF) quality sensor in vehicles equipped with a Cummins engine. This sensor measures both the temperature and quality of the DEF fluid.
What does the FMI (Failure Mode Indicator) 10 mean for SPN 3515?
FMI 10 indicates an abnormal rate of change for the DEF quality sensor reading. Other potential FMIs for SPN 3515 include 3 (voltage high), 4 (voltage low), and 2 (intermittent signal).
What vehicle makes and models can be affected by SPN 3515?
SPN 3515 is a generic J1939 code that can occur on various makes and models with Cummins engines, such as Volvo trucks, Kenworth trucks, Peterbilt trucks, and Case IH agricultural equipment.
What are the potential causes of SPN 3515 FMI 10?
Potential causes include a faulty DEF quality sensor, wiring issues between the sensor and ECM, contaminated or degraded DEF fluid, extreme temperatures affecting sensor readings, and rodent damage to wiring or the sensor.
What components make up the DEF quality sensor?
The DEF quality sensor is typically a combination sensor that integrates a DEF quality sensor, DEF temperature sensor, and DEF level sensor into one unit.
Where is the DEF quality sensor located?
The combination DEF quality sensor is located in the DEF tank and connects to the vehicle’s engine control module (ECM) via wiring.
What should I do if I encounter SPN 3515 FMI 10?
Do not continue driving the vehicle. Driving with a faulty DEF quality sensor can lead to inaccurate readings, improper DEF dosing, and potential damage to the SCR system. Have the vehicle towed to a dealer or qualified repair shop for diagnosis and repair.
How is SPN 3515 diagnosed?
Diagnosis involves retrieving fault codes with a scan tool, visually inspecting the sensor and wiring, testing the sensor’s resistance, checking DEF fluid quality with a refractometer, and performing a wiggle test on wiring to check for intermittent faults.
What are the repair solutions for SPN 3515?
Repair solutions depend on the root cause and may include replacing a faulty sensor, repairing damaged wiring, draining and refilling contaminated DEF fluid, or fixing rodent-damaged wiring and installing deterrent tape.
How can I prevent SPN 3515 faults?
Prevention measures include using only API-certified DEF fluid from reputable suppliers, avoiding storing DEF for over 12 months, keeping the DEF tank area clean, regularly inspecting wiring, and promptly addressing any rodent issues.
What are the typical costs associated with diagnosing and repairing SPN 3515?
Costs can vary but may include a diagnostic fee of $100-200 USD, a replacement combination DEF sensor for $500-800 USD, DEF fluid at $3-6 USD per gallon, and wiring repairs from $100-300 USD.
Are there any other fault codes potentially related to SPN 3515?
Yes, related fault codes may include SPN 1761 (DEF tank temperature sensor), SPN 3031 (DEF tank level sensor), SPN 3226 (DEF pump), and SPN 4094 (reductant system performance).
Can SPN 3515 cause the engine to derate or shut down?
Yes, if the DEF quality sensor issue is not addressed promptly, it can lead to improper DEF dosing, which may trigger engine derate or shutdown to prevent damage to the SCR system.
How often should the DEF quality sensor be inspected or replaced?
The DEF quality sensor should be inspected during regular maintenance intervals, such as every 50,000 miles or 1,500 hours of operation. Replacement intervals may vary by manufacturer but are typically recommended every 150,000-200,000 miles.
Can using off-brand or contaminated DEF fluid cause SPN 3515?
Yes, using non-API-certified, off-brand, or contaminated DEF fluid can lead to inaccurate sensor readings and trigger SPN 3515. Always use high-quality, API-certified DEF fluid from reputable suppliers.
What is the normal operating temperature range for DEF fluid?
DEF fluid has a freezing point of 12°F (-11°C) and should be stored between 40°F (4°C) and 77°F (25°C) for optimal shelf life. The normal operating temperature range for DEF in the vehicle tank is typically between 32°F (0°C) and 140°F (60°C).
How does extreme temperature affect the DEF quality sensor?
Extreme temperatures, both hot and cold, can affect the accuracy of DEF quality sensor readings. Freezing temperatures may cause DEF to crystallize, while high temperatures can degrade the fluid faster. The sensor is designed to operate within a specific temperature range.
What is the expected lifespan of a DEF quality sensor?
The lifespan of a DEF quality sensor can vary depending on factors such as operating conditions, maintenance, and DEF fluid quality. On average, a DEF quality sensor may last 150,000-200,000 miles or 5-7 years before requiring replacement.
Can a malfunctioning DEF quality sensor cause environmental issues?
Yes, a faulty DEF quality sensor can lead to improper DEF dosing, which may result in higher NOx emissions from the exhaust system. This can have a negative impact on the environment and may violate emissions regulations.
What should I do if I suspect rodent damage to the DEF quality sensor wiring?
If you suspect rodent damage, visually inspect the DEF quality sensor wiring and connectors for signs of chewing or nesting materials. Repair any damaged wiring, replace the sensor if necessary, and install rodent deterrent tape or mesh covers to prevent future damage.